It has been known that, in a long-distance coaxial transmission line, the line loss generally increases with frequency. Thus, equalizers are inserted into suitable portions of such a transmission line for flattening the amplitude-frequency characteristics thereof, and it is desirable to make the equalizer controllable. Conventional equalizers are used to restore signals to their original signal amplitude level after being transmitted over a cable within a wideband RF range. During operation, the cable is subjected to different cable temperatures within a certain cable temperature range.
Conventional equalizers which are used to compensate for temperature changes which affect amplitude-frequency characteristics over a wideband RF range are usually complicated in design, and typically incorporate transistors which require an external power source. Thus, the reliability of such equalizers is questionable because they are subject to power failure or other failures due to the nature of the complicated design.